DOH: Antigen test not for tourists, workers

HIGH-RISK In this photo taken last month, high-risk individuals, among them medical, security and essential services front-liners, are screened for COVID-19 as the city prepares to welcome tourists. —JEAN NICOLE PAUS/CONTRIBUTOR

BAGUIO CITY, Benguet, Philippines — Rapid antigen test for detecting the coronavirus may not be the ideal mass diagnostics tool for frequent travelers, cross border workers and tourists as the government had hoped, a Department of Health (DOH) official said.

Rapid antigen kits produced in South Korea failed to detect disease carriers with the same accuracy as the reverse transcription-polymerase chain reaction (RT-PCR) test, according to initial results of a Baguio validity study that was presented to the city council on Monday.

The study was commissioned by the DOH in September to establish whether the antigen test should be used on travelers who cross multiple borders. It was changed into a field study of the same antigen brand bought by the Department of Tourism for Baguio when it allowed residents of the Ilocos region to visit the city this month.

An antigen test costs a third of the P3,500 for RT-PCR tests, which tourists must shoulder as part of an entry screening in Baguio.

Rapid antigen diagnostics kits test for viral proteins (or antigens) and can process throat swab samples in 15 to 45 minutes, or up to three hours in more comprehensive kits.

Recommendation

The RT-PCR test, which remains the most sensitive diagnostic tool in detecting COVID-19, processes nasal and throat samples for evidence of nucleic acid associated with SARS-Cov-2, the virus causing the disease.

Laboratories release RT-PCR test results between 48 and 72 hours after specimens are taken.But in a recommendation released on Sept. 29, the DOH health technology assessment committee (HTAC) said the antigen was “most useful when patients are manifesting symptoms.”

It may “not be efficient” when testing people who do not show any symptoms and who have no history of exposure to the disease, said Dr. Angelita Pangilinan, the DOH Cordillera director.“HTAC does not recommend the antigen for indiscriminate use in mass screening. It is not recommended for mass screening of tourists,” Pangilinan said.

According to her, the rapid antigen test was used in Baguio last month during a series of outbreaks because “it is best used to identify current, acute or early infections.”

Soaring cases

Coronavirus cases in the city soared to 1,222, including 77 reported on Monday, due largely to transmissions near the slaughterhouse, the meat market and a building that houses police trainees. Close to 600 patients, including 100 police trainees, have been isolated for treatment.

The antigen was applied to 869 residents who interacted with the new patients, said Dr. Donabel Tubera-Panes, chief of the infectious disease unit of the city health services office. The patients were made to undergo parallel RT-PCR tests to compare the results.

Although 8 percent of test results have yet to be released, the antigen detected 77 carriers (10 percent) out of the 799 processed results. The RT-PCR tests, however, uncovered 117 carriers (15 percent) from the same batch of test subjects, Panes said.

Citing the study, Pangilinan also said the antigen test tended to be more effective when used on people who displayed symptoms five days after contracting the virus.

—Vincent Cabreza